Folding door



Feb 7 H967 G. M. ANDQEWS ETAL Sg FOLDING DOOR Filed Nov. 50, 1964. 7Sheets-Sheet 1 ,f /3/6\:V 55/- l ISG 53 I O l k H2 |5 '11 L [l y 1 1s 1|,l l I 1 y l lof l l i INVENTORS. GEORGE M. ANDREWS.

CHARLES. VJ. GISSON. m W

ATTORNEY.

7 Sheeis-Sheet 2 Feb. 7, 1967 e. M. ANDREWS ETAL FOLDING DOOR Filed Nov.:5o. 196A.

JNVENTORS.

GEURGE M, ANDREWS.

CHARLas w. GIBSON. BY f STTORNEY.

Feb 7. 3967 G. M. ANDREWS ETAL mm FOLDING DOOR Filed Nov. 30, 1964 7Sheets-Sheet 3 INVENTORS. GEORGE Pil. ANDREWS. CHARLES W. GIBSON.

ATTORNEY.

Feh 7, 1967 G. M. ANDREWS ETAL E FOLDING DOOR 7 Sheets-Sheet 4 FiledNOV. 30, 1954 WIG. 4

,INVENTORS GEORGE M. NDREWS. CHARLES W. GIBSGN.

TTRNEY.

Feb 7, 967 G. M. ANDREWS ETAL @3102,93

FOLDING DOOR Filed Nov. 30, 1964 7 Sheets-Sheet 5 WIG. 5

IN VEN TORS.

GEORGE M. NDREWS. BY CHARLES W. GBSON.

ATTORNEY.

Feb 7, 3967 G. M. ANDREWS ETAL 3,302J59 FOLDING DOOR Filed Nov. 30, 1964'7 Sheets-Sheet 6 l: I i

VIII III V INVENTORS. GEORGE M. ANDREWS. CHARLES W. GIBSON.

STTORNE?.

Feyo 7, i967 e.. M. ANDREWS r-:TAL 393029593 FOLDING DOOR Filed Nov. 30,1964 '7 Sheets-Sheet 7 R" 2;.. @im 25 m; L@ n IN VEN TORS. GEORGE M.ANDREWS. BY CHARLES W. GIBSON.

TTORNEY United States Patent Oiltice 3,302,691 Patented-Feb. 7, 19673,302,691 FOLDING DOOR GeorgeM. Andrews, Syracuse, N.Y., and Charles W.

Gibson, Bloomingdale, Mich., assiguors to Vega Industries, Inc.,Syracuse, N.Y., a corporation of New vitork Filed Nov. 30, 1964, Ser.No. 414,676 7 Claims. (Cl. 160-206) This invention relates to a foldingdoor structure. Such structures consist of at least one pair of panelshinged together along their vertical edges, one panel having a hingestructure at, or adjacent to, its free vertical edge, and Athe secondpanel being provided at, or adjacent to, its free vertical edge withguide rollers movable in upper and lower tracks. For door openings ofsubstantial width, a second pair of panels may be employed. Such doorstructures are used extensively for closures for door openings in theinterior of buildings, for example, closet door openings. Such doorstructures have Ithe advantage in requiring less than one-half of theswing space occupied by conventional doors. However, prior folding doorsembodied a relatively heavy construction, which necessitated theservices of professionalmechanics to install the doors, and often thedoor structures became warped or twisted causing them to bind and becomeotherwise diicult to operate.

This invention has an object a folding door structure embodying a lightweight structure which is particularly economical to manufacture, whichis particularly easy to open and close, and which will not bind evenunder adverse conditions of mis-use.

The invention has as a further object a folding door structure whereinythe mechanism on which the doors are hinged and guided is convenientlyadjustable to effect proper alignment of the door panels and ease ofoperation, even though the door opening is out of square, which is oftenthe case.

The door structure of our invention may be shipped in compact form andquickly installed by a non-skilled person by the employment of only ascrewdriver.

The invention consists in the novel features and in the combinations andconstructions hereinafter set forth and claimed.

In describing this invention reference is had to the accompanyingdrawings in which like characters designate corresponding parts in allthe views.

FIGURE 1 is an elevational view of the inner side of a two-panel doorembodying our invention and including the contiguous portion of the doorframe.

FIGURE 2 is a view similar to FIGURE 1 with the door panels in full openposition and illustrating the upper track inclining upwardly to theleft, due to the out of square condition of the door opening.

FIGURE 3 is an enlarged view of the upper right-hand portion of thestructure shown in FIGURE 1.

FIGURE 4 is an enlarged view of the lower right-hand portion of FIGURE1.

FIGURE 5 is an enlarged view of the upper left-hand portion of FIGURE 1.

FIGURE 6 is an enlarged view of the lower left portion of FIGURE 1.

FIGURE 7 is a view taken on line 7 7, FIGURE 4.

FIGURE 8 is a View taken on line 8 8, FIGURE 3.

FIGURE 9 is a view taken on line 9 9, FIGURE 5.

FIGURE l is a view taken on line lil-10, FIGURE 6.

FIGURE ll is a perspective view of the bracket structure for the lowerpintle pin.

FIGURE l2 is a view taken on line 12 12, FIGURE 3.

FIGURE 13 is a view taken on line 13 13, FIGURE l.

The door structure includes at least one pair of panel membersdesignated generally 10, 11. Each of these members consists of arectangular frame formed of tubular side members 13, and tubular top andbottom cross members 14. In the structure shown, the tubular members 13,14 are formed of sheet metal bent up to form a tube, rectangular incross section, see FIGURES 7-10. The exterior or front side of thesemembers is bent outwardly and formed with a ange 17 spaced from thesides 16. The inner side 18 is bent at right angles to form the outerwall 19 of the tubular member, which in turn, is formed with a ilangeZtl overlying the flange 17, and is then bent inwardly over the edge ofthe flange 17. This construction provides a channel about the margin ofthe outer side of the tubular frame member for the reception of theperimetric margin of a facing member 22, see FIGURE 7. A facing member23 of greater thickness may be formed about its edge with aslot toreceive the flanges 17, 20, as shown in FIGURE 8. This arrangementprovides a portion of the facing member 23, of reduced thickness,extending into the channel formed by the spacing between the side Wall16 of the tubular member and the flanges 17, 20.

The tubular members making up the frame of each panel are securedtogether at the upper and lower corners of the panels by-triangular-shaped gusset membersV 15. The gusset members 15 are formedof sheet metal and are attached to the tubular members 13, 14 as by spotwelding. Each gusset is formed with a rectangular opening 25. A portionof the metal removed from the opening 25 is bent inwardly to form a ange26, which is pierced to form two extrusions 27, 28, each of which isform-ed with an aperture, the axes of which extend vertically orparallel to the side members 13. The end members 14 areformed withapertures aligned with the apertures in the extrusions 27, 28.

The inner, upper, and lower corners of the panel frame structures arealso joined by triangular gussets 31. The gussets 31 are not formed withthe openings 25, but are formed along their abutting edges with earportions to form a hinge 32. One or more hinges are also attached to theinner side members 13. With this arrangement, the panel 1G is hingedlyjoined to the panel 11.

The door structure further' includes an upper track member 35 secured tothe header 36 of the door opening as by screws 37. There is a lowertrack member 38 mounted on the sill of the door opening as by screws 39.With the door installed, as shown in FIGURE l7 the panel 11 is hinged orpivoted for movement about a vertical axis adjacent the jam 40 of thedoor opening. The panel 10 is provided adjacent its outer free edge withguide rollers movable in the upper and lower tracks 35, 38. The pivot lmounting for the panel 11 includes an upper pintle pinv 43, slidablymounted inthe upper gusset memberlS of the panel 11. This pin isslidably mounted in the aperture of the extrusion 28, and thecorresponding aperture in the upper cross member 14, see FIGURES l, 3,and 8. The' pin 43 is provided with a collar or stop member 47, and ahelical compression spring 48 is interposed between the interned flange26 of the gusset member 15, and the collar I 47, and acts to urge thepin yieldingly upwardly. The upper end portion 44 of the pin 43 is ofreduced diameter and extends into a laterally extending flange 45 of abracket 46 mounted in the upper track 35.

VThe upper track member 35 is'formed with depending side walls 5t), 51to provide a roller receiving slot. The side wall 5t) is formed alongits lower edge with an inwardly extending ange 52, see FIGURE 8. Theside wall 51 is formed with an inwardly extending ilange 53 extending ina plane above the flange 52. The bracket 46 is formed of sheet metal andhas a top wall 55 and depending side walls 56, 57. The side wall 57 ispositioned on the flange 53 and the side wall 56 is positioned .on theflange 52. The bracket has an end wall 60, and the flange i 45, in whichthe pivot pin 43 is mounted, is a continuation of a depending end wall60. The top Wall 55 of the bracket 46 is formed with a punched extrusion61, which is threaded to receive a screw 62, see FIGURE 3. When thescrew is threaded through the top wall of the bracket, t-he end of thescrew engages the top wall `of the track 35 moving the sides 56, 57 ofthe bracket into engagement with the flanges 53, 52 of the track. Thisarrangement provides for adjustment of the bracket lengthwise of thetrack 55.

There is a pintle pin 67 slidably mounted in the lower corner gusset 15,and extends through the aperture in the extrusion 28 thereof and throughan aligned aperture in the lower cross member 14, whereby the pintle pin67 is arranged in axial alignment with the pintle pin 43. The lower endof the pin 67 extends through an aperture 70 formed in a bracket 71positioned in the lower track member 38. The aperture 70, see FIGURE ll,is of such diameter as to provide clearance for the pin 67. A retainingplate 73 is positioned lagainst the undersurface of the top wall of thebracket 71, and is provided with an aperture 74 of diameter comparableto the aperture 70. The aperture 74 communicates with a slot 75. Thelower end portion of the pin 67 is formed with a necked down portion 80,the diameter of which is slightly less than the width of the slot 75 inthe retaining plate. The retaining plate has a threaded aperture 81 toreceive a screw 82 which extends through an elongated opening 83 in thetop wall of the bracket 71. With this arrangement, the retaining plate73 can be moved lengthwise of the bracket and track 38 to bring itsaperture 74 in registration with the aperture 70 in the bracket topermit insertion of the pintle pin 67 Thereupon, the retaining plate 73is shifted to the left, FIGURE ll, so that the necked down portion 80 ispositioned in the slot 75 and, accordingly, the pintle pin is restrainedfrom vertical movement.

The lower track member 38 is formed with inclined side walls 85 having,at their upper edges, inwardly extending anges 86. The bracket 71 isformed along each side edge with an inclined flange 87. When the bracketis inserted in the lower track member 3S, a screw 88 is threaded into acounter-sunk aperture 89 in the top wall of the bracket, the lower endof the screw engages the bottom wall 90 of the track to clamp the sides87 `of the bracket against the sides of the track. This arrangement, asin the case of the upper pintle bracket, provides for adjustment of thebracket along the track 38.

The pintle pin 67 is provided with threads, the major portion of itslength from the upper end downwardly. A collar 93 is threaded on the pin67 and is held in adjusted position by a set screw 94. The collar 93engages the ange 26 of the gusset 15. A helical compression spring 95 isinterposed between the outer wall of the lower cross member 14, and thecollar 93 serves to yieldingly maintain the stop member 93 against theange 26 of the gusset 15, as shown in FIGURE 7. The purpose of the stopmember 93 is to vertically position the panel frame 11 to provide properclearance between the lower edge thereof and the lower track 38. Thisadjustment is made by loosening the set screw 94, and rotating the pin67. To make such operation convenient, the upper end of the pin isprovided with a screw driver slot 98.

With the structure described, the panels 10, 11 are pivotally mounted inthe door opening, and the panel 10 is hinged to the panel 11.

As previously stated, the panel is provided adjacent its free edge withupper and lower guide members to properly guide the panels duringopening and closing of the door structure. Referring now to FIGURES 1,6, and 10, a pin 100 is slidably mounted in the aperture of theextrusion 27 in the ange 26 of the lower gusset member 15, the pinextending through an aligned aperture in the wall 19 of the lower crossmember 14 of panel 10. The lower end of the pin 100 is necked down as at101, and a bottom roller 102 is journalled on the necked down portion101 of the pin, the roller being positioned in the lower track member38. The pin is provided with a stop collar 103, and a compression spring104 is interposed between this collar and the flange 26 of the gusset,thereby urging the pin downwardly against the roller 102 and the latteragainst the lower inclined walls 105 of the lower track.

Referring now to FIGURES 1, 5, and 9, there is a pin slidably mounted inthe upper left gusset member 15 of the panel 10, this pin also extendingthrough the aperture of the extrusion 27 in that gusset, and through thealigned aperture at the upper cross member 14. There are a pair ofrollers 111, 112 joumalled on the upper end of the pin 110, and the pinis restrained against downward movement by a head 113. The lower portionof the pin 110 is threaded to receive a stop collar 114, similar to thecollar 93. A compression spring is interposed between this collar, andthe flange 26 of the gusset member, and serves to yieldingly urge thepanel 10 upwardly. The upper roller 111 engages the upper flange 53 ofthe upper track, and the lower roller engages the lower ange 52. Thecollar 114 is adjusted axially along the pin 110 to a position where thespring 115 will give adequate support to the panel 10. The purpose ofthe spring 104, encircling the lower roller pin 100, is to maintain thelower end of the pin in engagement with the lower roller 102 underslight pressure, and to prevent any rattling of the door during theopening and closing thereof. Spring 115, in addition to providing asupporting force for the panel 10, also functions to prevent anylooseness or play between the pin 110 and the door panel and between therollers 111, 112 and the upper track member.

The mounting arrangement of the roller pins 100, 110 is an importantfeature of our invention. In actual practice, Imore often than not, dooropenings are not framed perfectly square, and with the header extendingparallel to the sill of the opening. In other door structures of thistype, it then becomes necessary to shim the upper track in order tobring it in parallel relation to the lower track. With our doorstructure, the header and sill can be out of parallelism to asubstantial degree, yet the upper track may be xedly secured directly tothe header. This arrangement permits vertical sliding movement of thepin 110 during the opening and closing of the door when the door openingis out of plumb. For example, in FIGURE 2, the upper track member 35slants upwardly to the left, the horizontal being indicated by thedotted line 117. In a situation of this kind, the roller -pin 110 simplyslides up and down during the closing and opening of the door, andwithout causing any binding during the operation of the door.

Referring to FIGURE 9, it will be observed that the lateral spacingbetween the track anges 51, 52 is such, relative to the diameter of therollers 111, 112, that there is a clearance between the side wall 51 andthe lower roller 112, and a clearance at 121 between the roller 111 andthe side wall 50. In other words, the rollers 111, 112 engage only theirrespective flanges 53, 52 and do not engage the opposite side wall ofthe track. This permits free rotation of the rollers 111, 112 in bothdirections, along the track, and this is true even `though considerablelateral pressure is exerted against the door panels.

With the construction described, the door structure is adapted to beshipped in a package form including the panels 10, 11, the upper andlower track sections, and the panel hanging hardware described. A rubberbumper is positioned in the upper track 35, and a similar bumper 131 ispositioned in the lower track 38, together with the roller 102. Thelower pintle bracket 71 is also positioned in the lower track member,and the upper pintle bracket is positioned in the upper track member.The pintle pins 43, 100 are mounted in the panel 11. The roller pins 67,100 are mounted in the panel 10. The rollers 111, 112 yare mounted onthe pin 110.

The door structure is installed by mounting the upper and lower tracks35, 38 on the header and sill of the opening. The panel assembly is thenangled to insert the rollers 111, 112 through an access opening 133formed in the upper track 35 in proximity to the end thereof, in whichthe pintle pin 43 will be mounted. At this time, the upper pintlebracket is moved toward the adjacent opening jam 40. When the rollers111, 112 have been thus insertedinto the upper track, the rollers aremoved toward the center of the track. The panel 11 is then manipulatedto bring the lower pintle pin 67 into the aperture 70 of the Alowerbracket and the plate 73 moved and locked in place by screw 82 tocaptivate the lower end of the pintle pin 67. Y

The upper pintle bracket is then moved in the upper track to locate theaperture in the flange 4S the same distance from the door jam 40 as thelower pintle pin 67. The upper Ipintle pin 43 is then inserted into theupper bracket. The door structure is shipped with a retaining pin 135inserted through an aperture 136 in the pin 43, at which time theaperture 136 is below the gusset ange 26. The retaining pin 135 is shownin dotted outline, FIGURE 3. Accordingly, all that is necessary to do isto remove the pin 135, and the compressed spring 48 moves the pintle pin43 upwardly into engagement with the upper pintle bracket.

The lower 4guide roller 102, which in shipment was captivated in thelower track section by the lower bracket and the rubber bumper, is movedalong the track to the left in the drawings so that the pintle pin 100may be positioned over it. This pintle pin is also provided with anaperture 138 to receive a retaining pin on the upper side of the gussetflange 26. Accordingly, by removing that retaining pin, the spring 104moves the pin 100 downwardly into engagement with the lower roller 102.

The door panels may then be moved laterally to center the same in thedoor opening by adjusting the upper and lower pintle brackets in theupper and lower tracks, and when this adjustment is eifected, the upperbracket is locked in place by screw 62, and the lower bracket is lockedin place by screw 88. When the upper bracket is secured in properposition, it -covers the access cutout 133 in the top track so that therollers 111, 112 cannot escape.

The door can be adjusted for height by simply turning the lower pintlepin 67 inthe stop member 93. When the height adjustment has beeneffected, the set screw 94 is tightened.

As the weight of the panels 10, 11 are increased substantially, as bymounted glass mirrors on the iinished panels 22, 23, the stop nut 114may be threaded upwardly to cause the spring 115 to exert a greaterforce on the gusset flange 26; these various adjustments being made toeffect easy and noiseless operation of the panels during the opening andclosing thereof.

The rubber bumpers 130, 131 serve to provide for a silent closing of thepanels and, also, to position the panels under a slight yieldingpressure when the panels are moved to closed position in order to makecertain that the panels remain in closed position. In this connection,it will be noted that the -access of the pintle in hinges 32 is locatedrearwardly of the plane of the pintle pins and roller pins, see FIGURE13. With this arrangement, the panels close snap fashion, the panelsforming a slight-ly over the center toggle arrangement so that the doorpanels remain in closed position.

The flange 140 on bracket 46 is engaged by the rollers 111, 112 when thedoor is actuated to open position, the flange 140 serving as a bumperstop, see FIGURE 2.

What we claim is:

1. A folding door structure for a door opening, an upper track memberixedly mounted to the header in the door opening and extending betweenthe jams thereof, said track member being formed with a roller receivingslot having inwardly extending side flanges extending in spaced parallelrelation, a lower track member formed with a roller receiving slot andbeing iixedly mounted to the sill of the opening and extending betweenthe jams thereof, a pair of first and second panel mem-bers hingedlyjoined along their vertical edges and being of vertical dimension forinsertion in said opening between said track members, the rst of saidpanels being provided with vertically aligned upper and lower pintlepins extending from the upper and lower edges of said rst panel inspaced relation to said hinged joint, the outer ends of said pins beingjournalled in said upper and lower track members, said upper pintle pinbeing axially slidable in said irst panel, spring means acting on saidpin to yieldingly urge the same upwardly, said lower pintle pin having astop collar member adjustable axially of the pin for engaging said firstpanel for the support of said first panel by said lower pintle pin,upper and lower roller pins mounted in said second panel of said pair inspaced relation to said hinged joint, said lower roller pin having aroller journalled thereon for movement along the slot in said lowertrack member, said upper roller pin having a roller journalled thereonfor movement along the flanges of said upper track member, meansrestraining downward movement of said upper roller pin relative to theroller journalled thereon, said upper and lower roller pins beingaxially slidable in said second panel.

2. A folding door structure as defined in claim l, wherein said lowerpintle pin is slidably mounted in the lower edge structure of said rstpanel and a flange thereof spaced above said lower edge structure, saidstop collar member being positioned on said lower pintle pin below saidange, and spring means interposed be-tween said lower edge structure andsaid stop collar member and operable to yieldingly press said stopmember against said flange.

3. A Ifolding door structure as set forth in claim 1, wherein said stopcollar member is threaded on said lower pintle pin and means is providedfor interlocking said stop member to said pin.

4. A folding door structure according to claim 1, wherein said ange iscooperable with said stop collar member to restrain the same againstrotation relative to said lower pintle pin.

5. A folding door structure as set forth in claim 1, wherein a stopcollar member is mounted on said upper roller pin and being adjustableaxially thereof, a spring interposed between said stop collar member andsaid second panel for yieldingly supporting the same.

6. A folding door structure as set `forth in claim 1, wherein said upperroller pin is slidably mounted in the upper edge structure of saidsecond panel and in a ange thereof positioned 'below said upper edgestructure, a stop collar member carried fby said upper roller pin, and aspring interposed -between said stop collar member and said flange andoperable to yieldingly support said second panel on said upper rollerpin.

7. A folding door structure for a door opening, an upper track memberiixedly mounted to the header of the door opening and extending betweenthe jams thereof, said track member having spaced apart, verticallydisposed side walls, a roller supporting ilange formed on the innersurface of each of said side walls, said tlanges extending in spacedparallel relation in both the horizontal and vertical plane, a lowertrack member formed with a roller receiving slot and being xedly mountedto the sill of the opening and extending between the jams thereof, apair of iirst and second panel members hingedly joined along theirvertical edges and being of vertical dimension for insertion in saidopening between said track members, the rst of said panels beingprovided with a pair of vertically aligned pintle pins extending fromthe upper and lower edges of said panel in spaced relation to saidhinged joint, the ends of said pins being journalled in said upper andlower track members, upper and Ilower roller pins vertically mounted inthe second panel of said 7 pair in spaced relation to said hinged joint,said lower roller pin having a roller journalled thereon for movementalong the slot in said lower track member, said upper roller pin havinga pair of rollers journalled thereon in axially spaced apart relationeomplemental to the Vertical spacing `between said anges in said uppertrack member for movement along the anges, respectively, meansrestraining downward movement of said upper roller pin relative to therollers journalled thereon, the rollers journalled on said upper pinbeing of substantially equal diameter, said roller receiving flangesVbeing spaced inwardly from the contiguous side wall of said upper trackmember, whereby said rollers journalled on said upper pin do not engagethe side Wall of said upper track member, opposite to the flangesupporting each said roller.

References Cited by the Examiner UNITED STATES PATENTS 1,444,349 2/1923Leeds 160-196 2,860,701 11/1958 Wood et al. 160-199 2,943,675 7/1960Ford 160-206 3,019,836 2/1962 Leigh 160-199 3,042,960 7/ 1962 Spork.

3,205,982 9/1965 Chimienti 189-46 HARRISON R. MOSELEY, Primary Examiner.

D. L. TAYLOR, Assistant Examiner.

1. A FOLDING DOOR STRUCTURE FOR A DOOR OPENING, AN UPPER TRACK MEMBERFIXEDLY MOUNTED TO THE HEADER IN THE DOOR OPENING AND EXTENDING BETWEENTHE JAMS THEREOF, SAID TRACK MEMBER BEING FORMED WITH A ROLLER RECEIVINGSLOT HAVING INWARDLY EXTENDING SIDE FLANGES EXTENDING IN SPACED PARALLELRELATION, A LOWER TRACK MEMBER FORMED WITH A ROLLER RECEIVING SLOT ANDBEING FIXEDLY MOUNTED TO THE SILL OF THE OPENING AND EXTENDING BETWEENTHE JAMS THEREOF, A PAIR OF FIRST AND SECOND PANEL MEMBERS HINGEDLYJOINED ALONG THEIR VERTICAL EDGES AND BEING OF VERTICAL DIMENSION OFINSERTION IN SAID OPENING BETWEEN SAID TRACK MEMBERS, THE FIRST OF SAIDPANELS BEING PROVIDED WITH VERTICALLY ALIGNED UPPER AND LOWER PINTLEPINS EXTENDING FROM THE UPPER AND LOWER EDGES OF SAID FIRST PANEL INSPACED RELATION TO SAID HINGED JOINT, THE OUTER ENDS OF SAID PINS BEINGJOURNALLED IN SAID UPPER AND LOWER TRACK MEMBERS, SAID UPPER PRINTLE PINBEING AXIALLY SLIDABLE IN SAID FIRST PANEL, SPRING MEANS ACTING ON SAIDPIN TO YIELDINGLY URGE THE SAME UPWARDLY, SAID LOWER PINTLE PIN HAVING ASTOP COLLAR MEMBER ADJUSTABLE AXIALLY OF THE PIN FOR ENGAGING SAID FIRSTPANEL FOR THE SUPPORT OF SAID FIRST PANEL BY SAID LOWER PINTLE PIN,UPPER AND LOWER ROLLER PINS MOUNTED IN SAID SECOND PANEL OF SAID PAIR INSPACED RELATION TO SAID HINGED JOINT, SAID LOWER ROLLER PIN HAVING AROLLER JOURNALLED THEREON FOR MOVEMENT ALONG THE SLOT IN SAID LOWERTRACK MEMBER, SAID UPPER ROLLER PIN HAVING A ROLLER JOURNALLED THEREONFOR MOVEMENT ALONG THE FLANGES OF SAID UPPER TRACK MEMBER, MEANSRESTRAINING DOWNWARD MOVEMENT OF SAID UPPER ROLLER PIN RELATIVE TO THEROLLER JOURNALLED THEREON, SAID UPPER AND LOWER ROLLER PINS BEINGAXIALLY SLIDABLE IN SAID SECOND PANEL.